This invention relates to pulmonary-ventilator assemblies and more particularly to such assemblies in kit form capable of simple fast change over from large to small capacity ventilation modes, and visa versa.
Pulmonary-bellows-assemblies are typically used for forced ventilation of anesthetized human patients or animals undergoing surgery. The ventilating gas may contain carefully controlled amounts of oxygen, nitrous oxide or helium and must be kept sterile. Sterilization of the ventilation parts, like surgical instruments, is preferably accomplished by disassembly and subjecting the parts to steam but the plastic parts such as the plexiglass of commercial ventilators distort in steam and must be scrubbed with alcohol or other disinfecting agents.
In ventilation operation, the interior of the bellows 10 is connected to the patient's breathing system 11 as is illustrated in FIG. 1. The space between the bellows 10 and the surrounding bellows housing 12 is connected to the pneumatic driving control unit 14. The driving gas from the control unit 14 is usually air. During the inspiratory phase, the driving gas compresses the bellows 10 and forces the ventilating gas within the bellows 10 into the patient's breathing system 11. The absorber head 17 is a part of an anesthesia machine that removes the carbon dioxide from the exhaled gasses. During the expiratory phase the driving gas is released from the bellows housing 12 and the patient exhales into the bellows 10. When the bellows 10 reaches the maximum excursion, the pop-off valve 18 automatically opens and the excess breathing gas 19 escapes through the exhaust port 20.
The pressure over the upper surface of the valvediaphram 22 is always the same as that in the bellows housing 12 outside the bellows 10. The pressure acting on the lower surface of the diaphram 22 is always the same as the pressure within the bellows 10. The check valve 24 over exhaust port 20 is attached to the lower surface of the diaphram 22 and the pressure acting on the exhaustport side of the valve seat 24 is always ambient pressure.
During the inspiratory phase the driving gas exhaust valve 26 in the control unit 14 is closed and the driving gas generated by the flow controller 28 increases the pressure on the outside of the bellows 10. The driving gas is communicated to the top of the pop-off valve 18 via valve channel 30 and the pop-off valve 18 is held closed during the inspiratory phase. The driven pressure at the inside and outside of the bellows is the same.
During the expiratory phase the driving gas exhaust valve 26 opens dropping the pressure in pipe 32 to the ambient. The pressure outside the bellows drops, and the pressurized resilient lungs of the patient discharge back into the bellows 10 and when the bellows 10 becomes fully extended to or at the top of the housing 12 the pressure inside the bellows increases. At about 2 cm H.sub.2 O pressure the pop-off valve 18 opens so that the excess exhaled gas is vented to the ambient.
The appropriate size or capacity of the bellows for adult patients is about 1500 milliliters (ml) whereas for small children or smaller animals a smaller bellows capacity, e.g. 300 ml, is needed. One commercially available ventilator is provided with a small bellows and bellows housing that can be substituted for the standard adult larger ones. A small bellows holder is seated on top of the adult bellows base. The housings are alternately mountable to the base using a large annular rubber piece seal. The large U-shaped cross section is designed to seal against the molded and irregular surface of the plexiglass housings, which seal tends to leak and to lack great reliability. It also tends to bind at disassembly. This ventilator construction also has the disadvantage that when the pediatric bellows holder is mounted in place, the adult bellows cannot be used, and the pediatric bellows holder must be removed to mount and use the large bellows. In that commercial ventilator the housings each have a square flange and four bolts to secure them to the base, making disassembly and exchange additionally complicated and time consuming.
Another well known commercial ventilator has a wire cage that is fitted over the bellows housing and attached to the base to firmly mount and seal the housing to the base. No provision is made for a small pediatric bellows. A later model of that exclusively adult ventilator provides a housing with four protruding pins close to the lower rim and a retainer ring which has a flange for fitting over the pins to secure the housing. The edge of the flange engages three protruding screws integral with the base. To mount this molded plexiglass housing, it is pushed downward to seal against a large annular U-shaped rubber piece, as in the ventilator described above. The ring is fitted over the housing engaging the housing pins. Then the ring is oriented to allow the screw heads to fit through notches provided therefore in the ring flange. The ring is then twisted to secure the ring and thus the flange to the base.
It is an object of this invention to provide a pulmonary ventilator kit capable of being simply and quickly assembled with a large or small bellows and a corresponding large or small housing.
It is a further object of this invention to provide such a ventilator kit wherein said large and small housings are each mountable and reliably sealable to the same peripheral region of the base.
It is yet a further object of this invention to provide a small bellows adaptor capable of being easily fitted and reliably sealed to the base and which adaptor may be locked securely and safely in position by the mounting of the small housing.